!lfgend should continue to work in when the user's role is removed

[oliverphardman]

If some idiot mod decides to delete an lfg role, this will result in the bot malfunctioning.

Currently !lfgend will have the bot scan the DB for the session based on the user's role ID. This is probably still a good idea, but if a role is removed by accident !lfgend will not work properly. If we have !lfgend stop sessions based on the channel it is called in or the user that runs it we can avoid this problem.